1. Field of the Invention
This invention is concerned with a catalytic process for reaction of phosphorus halides with thiols.
2. Description of the Prior Art
It has been proposed in the art, such as in U.S. Pat. No. 2,955,803, to effect the reaction between a phosphorus halide (e.g., PCl.sub.3) and a thiol (e.g., butanethiol) or phenol using a hydrogen halide acceptor, such as triethylamine or an alkali-metal hydroxide. This procedure is disadvantageous because it requires tedious product separation steps and, to be economically feasible, would require recovery and regeneration of the hydrogen halide acceptor.
Efforts have been made to remove hydrogen halide by applying a slight vacuum to the reaction system. This technique is commercially unattractive, because the reaction is sluggish and has a long induction period before hydrogen halide starts to evolve. This has been overcome to some extent by adding water to the reactants, but the reaction is still sluggish. Furthermore, water leads to turbidity and odor recurrence in the product and to the formation of pyrophoric sludges.
By the use of a formamide as a catalyst, the induction period is virtually eliminated. The formamide does not appear to be consumed in the reaction.